[sdiy] 1v /oct with ADC question

rsdio at audiobanshee.com rsdio at audiobanshee.com
Sat Dec 3 01:28:02 CET 2016

Yes, it does seem a little bizarre since all other CV was disconnected from any real analog source. Perhaps they did not want to incur the latency of a scanned keyboard and DAC. With the design as they have it, the keyboard can directly control the VCO, even if the modulation for the VCO that is added comes from a DAC.

I can't tell from the Source schematic - because it's broken across several pages and hard to read quickly - but it's theoretically possible that the keyboard CV could be applied directly to CV mixers for each VCO control input. Octave, Pitch Bend, Modulation, Pitch Envelope and other CV sources would be mixed in (added), but those could come from a DAC in some cases, as opposed to live, analog CV.

I also wonder whether Sequential Circuits and/or E-mu had a patent on keyboard scanning at the time. They certainly invented it. What we take for granted now was not always standard.


On Dec 2, 2016, at 3:05 AM, Tom Wiltshire <tom at electricdruid.net> wrote:
> It's a bizarre way of doing it. If you've got a microprocessor, why not just scan the keyboard, and then output the voltage to the DAC? (Like the Pro-One or SH-101 does) Maybe they ran out of pins.
> On 2 Dec 2016, at 05:41, Michael E Caloroso <mec.forumreader at gmail.com> wrote:
>> The Moog Source has no ADC.
>> The keyboard is analog, but the system is using a comparator with the
>> keyboard CV at one input and a successive approximation voltage
>> generated from the DAC at the other input to derive the key note.  The
>> comparator output is simply a logic input to the CPU.
>> That's how Moog got away without using an $$$ ADC.
>> MC
>> On 12/1/16, Tony K <weplar at gmail.com> wrote:
>>> Have a look at the Moog Source keyboard circuit. As far as I am aware it is
>>> the only analog keyboard to ADC to DAC again. I love that synth.
>>> Tony K
>>> On Dec 1, 2016, at 1:46 PM, Mike HEQX <mike at heqx.com> wrote:
>>>> This makes a lot of sense. Never thought of using a DAC after the ADC to
>>>> generate the CV.
>>>> I would never have been able to make it work otherwise. So now I know for
>>>> the next time.
>>>> I can't wait to make it play notes for the first time.
>>>> Thanks to all who responded. Everyone had a different view, and all were
>>>> very valuable.
>>>> Mike

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